Autor: Lemaire
• ETYMOLOGY
“Star plant” because of the typical shape of some species within the genus.
• DESCRIPTION
A genus of usually solitary, highly variable plants, flattened, globose or elongated to shortly columnar, mostly covered with flaky scales (trichomes), some with spiny scales, with well defined ribs or with very elongated tubercles (A. caputmedusae). Spines present or absent depending on the species. Flowers diurnal, self sterile, apical, funnel-shaped, yellow, some species have a red centre, pollinated by bees. Fruits globose with persistant scales, dehiscent when ripe. Seeds brown, helmet-shaped, light. Seed dispersal by hydrochory (streaming water) or myrmecochory (by ants).
The genus is subdivided into three synthetic sub-genera:
– Astrophytum – includes species with yellow flowers and fruits having an apical dehiscence (A. myriostigma, A.
ornatum).
– Neoastrophytum – includes species with bicoloured flowers (red or orange centre) and fruits with a basal
dehiscence or irregular and indehiscent (A. asterias, A. capricorne, A. coahuilense).
– Stigmatodactylus – Includes the only tuberculate species of the genus (A. caput-medusae).
• HABITAT
The genus Astrophytum grows from 100 m (A. caput-medusae) up to 2000 m in altitude, in a very scattered habitat
in the desert of Chihuahua, on the central plateau of Mexico and the southern plains of Texas, United States,
depending on the species, often in the shade among grasses and bushes, in the matorral, (vegetation association of
herbaceous plants, succulents and shrubs) on rocky grounds, in cracks, on steep slopes, limestone mounds, gravel
and clay alluvial soils, bed of dry lakes or in ravines of calcareous rocks, together with other Cactaceae and Bromeliads (Hechtia spp.). The xerophytic vegetation allows species to take advantage of a good period of sunshine. In this region, the annual temperature does not vary much, but the rainfall is very irregular. The winter is characterized by high thermal amplitudes (differences of temperature between day and night), and a few frosty nights are not uncommon.
• DISTRIBUTION
Mexico (Coahuila, Durango, Guanajuato, Hidalgo, Nuevo-León, Querétaro, San Luis Potosí, Tamaullpas, Zacatecas), USA (Texas).
Currently 6 recognised species + 2 subspecies:
– Astrophytum asterias* (Zuccarini) Lemaire 1868
– Astrophytum capricorne* (A.Dietr.) Britton & Rose 1922
– Astrophytum caput-medusae* (Velasco & Nevarez) Hunt 2003
– Astrophytum coahuilense (H.Moeller) K.Kayser 1932
– Astrophytum myriostigma* Lemaire 1839
– Astrophytum myriostigma subsp. potosinum (H.Moeller) K.Kayser 1932
– Astrophytum myriostigma subsp. tulense K.Kayser 1932
– Astrophytum ornatum* (DC.) Britton & Rose 1922
References: "TAXONOMY of the CACTACEAE" - ISBN 978-84-617-3723-9 (Vol. 1)